In a large bowl, stir together the flour, sugar, cinnamon, baking powder and salt.
In a smaller bowl, whisk together the milk, eggs and oil; add to the dry ingredients and whisk just until combined.
Set a large, heavy skillet over medium-high heat and drizzle it with oil, then swirl it to coat the pan. Turn the heat down to medium-low and wipe the pan out with a paper towel.
Cut the apples crosswise into 1/4-inch thick slices; remove the middle core (if needed) with the tip of a sharp knife. Dip the apple slices into the pancake batter and place in the hot pan; cook, turning with a thin spatula, until golden on both sides. Repeat with remaining apples and batter.
If you need to keep the finished pancakes warm, keep them uncovered on a plate in a 250ºF oven. Serve warm, with butter and maple syrup.